[Zhengyu Gao]

Hello everyone,

I have to make a transient heat transfer simulation of a loudspeaker by FLUENT. And the moving boundary is controlled by the UDF showed below. These two UDF code make the axis stretching and the dust cap oscillating. Two UDF codes function well, however, after many times iteration node A on axis moves faster than node A on dust cap. So minus volume error occurred.

I think it is because the two boundaries are controlled by two UDF codes, and error occurred. I tried many ways to combine these two UDF code together(use if else if, switch ...), but I don't know what to put into "if()", in other words, I don't know how to define the condition when to use code stretching and code oscillating.

PS I tried remeshing, it doesn't work.

I attached the pictures of UDF code, description of the moving dust cap and the deformation of grids. I hope it will help you to understand this problem.

please help me ! thanks in advance